1. Field of the Invention
The present invention relates to a pre-ignition estimation control device for an internal combustion engine which is mounted in a vehicle or the like in order to prevent pre-ignition at the time of idling stopping for stopping a vehicle automatically.
2. Background Art
In a spark ignition type internal combustion engine with a high compression ratio, pre-ignition which causes combustion noise or an output fluctuation may occur. The pre-ignition refers to a phenomenon in which a pressure fluctuation in a combustion chamber of the internal combustion engine caused by combustion becomes excessively large. Generally, pre-ignition occurring before spark ignition is known. In addition to this pre-ignition, there is also a phenomenon, such as pre-ignition in which the temperature of the air-fuel mixture (mixed gas of air and fuel) in the combustion chamber becomes high by compression and the air-fuel mixture self-ignites as a result, or pre-ignition in which the tip of a spark plug, a deposit, or the like becomes a hot spot causing ignition. In addition, knocking in which end gas around the combustion chamber self-ignites in a combustion process after ignition is also known.
Such phenomena may not only cause noise or vibration but also damage the combustion chamber of the internal combustion engine and as a result, the internal combustion engine may stop operating eventually. In addition, it is known that pre-ignition frequently occurs at the starting of the engine.
For this reason, methods of preventing pre-ignition by estimating the occurrence of pre-ignition from environmental conditions or operating conditions have been proposed.
One of the known pre-ignition preventing methods is to prevent pre-ignition at the starting of the engine by determining pre-ignition, which occurs at high temperature under the low rotation speed and the high load, from the temperature and the operating state of the internal combustion engine and reducing the actual compression ratio according to the temperature increase (for example, refer to Patent Document 1).
Moreover, as a method of preventing pre-ignition at the time of idling stopping (automatic idling stopping), a self-ignition occurrence region is set with the engine temperature information as a parameter, and the temperature information is acquired and at the same time it is determined whether or not the value of the acquired temperature information is within the self-ignition occurrence region. Then, the engine is immediately restarted when it is determined that the value of the acquired temperature information is within the self-ignition occurrence region during automatic stopping of the engine, and the cooling device stops after automatic idling stopping. In this way, the occurrence of pre-ignition at the restarting of the engine is prevented (for example, refer to Patent Document 2).    [Patent Document 1] JP-A-2009-114973    [Patent Document 2] JP-A-2007-120448
Patent Document 1 discloses that pre-ignition at the starting of the engine is prevented by determining the ease of occurrence of pre-ignition and setting the actual compression ratio according to this at the starting of the engine. In the method disclosed in Patent Document 1, however, the intake-air temperature, the coolant temperature, and the octane rating of fuel are assumed in regard to the ease of occurrence of pre-ignition, but these are considered independently. That is, the ease of occurrence of pre-ignition under complex conditions including the above is not taken into consideration. Since there are many conditions in which pre-ignition occurs easily, it is necessary to set indices related to the ease of occurrence of pre-ignition in consideration of each of these conditions. In particular, at the restarting of the engine after automatic idling stopping, the occurrence of pre-ignition becomes especially easy since the engine is started at the high engine temperature.
Patent Document 2 discloses a method of determining the ease of occurrence of pre-ignition on the basis of the temperature. A temperature at which pre-ignition may occur when a fuel with a high octane rating is used is different from that when a fuel with a low octane rating is used. Accordingly, the temperature set on the assumption that a fuel with a high octane rating is used is too high for a fuel with a low octane rating. As a result, pre-ignition may occur. On the contrary, the temperature set on the assumption that a fuel with a low octane rating is used is too low for a fuel with a high octane rating. As a result, it may be determined that a possibility of the occurrence of pre-ignition is low.